I have heard of Thunderbird. But over the years, I simply didn't log into email using any of my old, rooted phones. I was curious if it had been safe.. or had been safe but was sold or was up to something shady. As many of these companies start out with good intentions and end up selling or doing a 180 when tempted.
In fact, I really only used my rooted phones for calls and texts. Occasionally listening to or watching something when enabling the appropriate app. With GrapheneOS, I've been trying things that I would usually just skip with a typical Android.